Electronic component mounted on a flat substrate and padded with a fluid filler

ABSTRACT

A method of padding an electronic component, mounted on a flat substrate, with a fluid filler, in which the fluid filler that is applied in a tight-fitting manner to the electronic component mounted on the substrate. The arrangement composed of substrate and electronic component is then heated. The substrate is provided with at least one through orifice in the area of the electronic component prior to applying the filler. The filler is applied at the end of the through orifice facing away from the electronic component.

This application is a continuation of U.S. patent applications Ser. No.09/516,605 filed on Apr. 3, 2000, now U.S. Pat. No. 6,445,074 issued onSep. 3, 2002, and Ser. No. 09/160,889 filed on Sep. 25, 1998, now U.S.Pat. No. 6,057,178.

FIELD OF THE INVENTION

The present invention relates to a method of padding an electroniccomponent, mounted on a flat substrate, with a free-flowing filler, inwhich the fluid filler is applied in a tight-fitting manner to theelectronic component mounted on the substrate and flows into thearrangement composed of the substrate and electronic component under theeffect of heat.

BACKGROUND INFORMATION

The document “Adhesive Dispensing for Flip Chip-on-Board,” ElectronicPackaging & Production October 1995, Advertising Insert pp. 9-11describes a method of padding an electronic component. In this method,the electronic component, which may be a semiconductor chip, forexample, is padded with a free-flowing filler after being mounted on aflat substrate, for example, on a printed circuit board, so that thefiller is linearly applied to at least one edge of the electroniccomponent using a dispenser. Under the effect of heat, the fillerbecomes fluid and penetrates by capillary action into the space betweenthe electronic component and the substrate. Additional amounts of fillerare then applied to those edges of the electronic component along whichno filler was previously applied, so that a meniscus-shaped seal isachieved on all the edges of the electronic component.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for padding anelectronic component mounted on a flat substrate with a free-flowingfiller that is relatively easy to accomplish.

To achieve this object, the substrate is provided with at least onethrough orifice in the area of the electronic component prior to theapplication of the filler, and the filler is applied on the end of theorifice facing away from the electronic component. The substrate may bea printed circuit board or foil, a ceramic substrate, or a load frame,for example; the electronic component is a flip chip or a ball gridarray, for example. Filler is understood as being a mixture of resin andinorganic additives or particles.

One advantage of the invention is that when padding the electroniccomponent, the filler penetrates underneath the electronic componentinto the space between the component and the substrate, so the fillerexpands in the space basically from the inside out in a way that all theair is displaced from the space between the electronic component and thesubstrate, while complete padding is achieved. Padding is donerelatively rapidly, since the filler can expand on all sides from the atleast one through orifice into the space between the electroniccomponent and the substrate. Another advantage is that in the methodaccording to the present invention, a meniscus-shaped seal forms byitself on all the edges of the electronic component, so that nosubsequent operation is required. The cost of providing the at least onethrough orifice is relatively low.

In the method according to the present invention, the filler can beapplied on the substrate if the electronic component is located as usualabove the substrate. This applies particularly in the case when only arelatively small amount of filler is to be applied to the substrate dueto a relatively small electronic component. This relatively small amountof filler does not drip off when heated, but is “sucked in” as knownupward by capillary action through the orifice into the space betweenthe electronic component and the substrate.

In the case of electronic components of typical dimensions, it isconsidered advantageous in the method according to the present inventionif the arrangement composed of the substrate and the electroniccomponent is brought into a position where the substrate faces upwardprior to applying the filler. In this embodiment of the method accordingto the present invention, a relatively large amount of the fillerapplied also remains in the area of the through orifice and can flowinto the space between the electronic component and the substrate underthe effect of heat and capillary action.

In order to pad the electronic component in a particularly rapid manner,pressure is exerted on the filler applied by the method according to thepresent invention.

In order to pad the space between the electronic component and thesubstrate as quickly and reliably as possible overall, it is consideredadvantageous if the through orifice is provided in the substratecentered with respect to the electronic component.

In the method according to the present invention it is not necessarythat the filler be applied onto the substrate using a dispenser. Thefiller can be applied by pouring, as long as the arrangement composed ofthe substrate and electronic component faces upward.

In the method according to the present invention, the through orificecan be advantageously used as a reservoir for the required amount offiller if the through orifice is sufficiently large. The filler thatbecomes fluid under the effect of heat cannot then expand on the side ofthe substrate facing away from the electronic component, but remains inthe through orifice.

It is, however, also possible to provide the substrate with anring-shaped piece mounted at the end of the through orifice facing awayfrom the electronic component.

With the method according to the present invention, the filler can alsobe applied by pressing or stamping, in addition to applying it with adispenser. Spraying the filler onto the substrate on the end facing awayfrom the electronic component of the through orifice is also possible.

The present invention also relates to an arrangement with a flatsubstrate and an electronic component mounted on it, with the spacebetween the electronic component and the substrate being padded with afluid filler.

In order to design such an arrangement so that it is easy tomanufacture, at least one through orifice is provided in the substrateunder the electronic component for applying the filler.

If a single through orifice is provided for the arrangement, this ispreferably centered in the substrate with the electronic component.

In the arrangement according to the present invention, the throughorifice has a volume that is at least equal to that of the fillerrequired for padding the electronic component.

In the arrangement according to the present invention, the volume in thearea of the through orifice can be prepared so that the through orifice,configured as a through hole, for example, has a cross-section of aproper dimension. It is considered particularly advantageous if thethrough orifice, on its side facing away from the electronic component,has a pot-shaped widening.

The volume required for holding the fluid filler can also be provided inthe area of the through orifice in the arrangement according to thepresent invention by providing a ring-shaped piece mounted on thethrough hole on its side facing away from the electronic component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a device for carrying out the methodaccording to the present invention with an arrangement including asubstrate and an electronic component shown in cross-section.

FIG. 2 shows an arrangement including a substrate and an electroniccomponent padded by the method according to the present invention.

FIG. 3 shows another arrangement including a substrate and an electroniccomponent also padded by the method according to the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a transport device 1, with which an arrangement 2 includinga substrate 3 and an electronic component 4 mounted on it is transportedinto the operating range of a dispenser 5. Arrangement 2 of a substrate3 and an electronic component 4 is positioned on transport device 1, sothat substrate 3 is located above electronic component 4.

As FIG. 1 further shows, electronic component 4 is connected tosubstrate 3 in the area of electrical contacts 6 and 7 formingarrangement 2 and is brought into the range of dispenser 5 in this form.Prior to this, a through orifice 8 is provided in substrate 3, at thecenter of electronic component 4. If arrangement 2 thus prepared andheated is brought into the position illustrated with respect todispenser 5, free-flowing filler is applied from the dispenser onto end9, facing away from electronic component 4, of through orifice 8. Theamount applied of filler 10 becomes fluid under the effect of heat andis drawn into the space 11 between substrate 3 and electronic component4 by capillary action. The air is displaced from the area of throughorifice 8 by filler flowing in. Ultimately, filler 10 is fullydistributed in space 11 and forms a meniscus-shaped seal at edges 12 and13 of electronic component 4.

Subsequently, substrate 3 is transported further either to pad withfiller another electronic component mounted or to pad another substratehaving an electronic component.

FIG. 2 shows an arrangement 20 padded according to the present inventionwith a substrate 21 and a mounted electronic component 22, in whichsubstrate 21 has a pot-shaped widening 26 at end 24, facing away fromelectronic component 22, of a through orifice 25. Filler 27 is filledinto this pot-shaped widening 26 in the padding process. The filler thathas become fluid under the effect of heat flows into space 28 betweensubstrate 21 and electronic component 22 by capillary action from theinside out and forms a meniscus-shaped seal at edges 29 and 30 ofelectronic component 22.

Arrangement 40 according to FIG. 3, which includes a substrate 41 and anelectronic component 42, basically corresponds to the arrangement 2 ofFIG. 1. It differs from the arrangement of FIG. 1 basically by the factthat substrate 41 is provided, on its side 44 facing away fromelectronic component 42, with a piece 45 surrounding through orifice 46forming a reservoir for filler 43.

What is claimed is:
 1. An arrangement, comprising: a flat substratehaving at least one through orifice; an electronic component mounted onthe flat substrate; a fluid filler padding a space between the flatsubstrate and the electronic component, the at least one through orificepositioned under the electronic component for applying the fluid filler,the at least one through orifice having a volume that is at least equalto an amount of fluid filler needed for padding the electroniccomponent; and a ring-shaped piece mounted on an end of the at least onethrough orifice that faces away from the electronic component andforming a reservoir for the fluid filler.